Influence of different coating structures on the oxidation resistance of MoSi2 coatings

Two different structures of MoSi2 coatings were prepared on Niobium based alloys by using a two step process. The as-deposited type(a) MoSi2 coating structure consists of a MoSi2 layer on the surface and a NbSi2 layer underneath, while the type(b) MoSi2 coating consists of an outer MoSi2 layer and an inner unsiliconized Mo layer. The oxidation behaviors of the two different types MoSi2 coatings were examined at 1200 °C for 100 h in air, and the mass gains of type(a) and type(b) MoSi2 coated specimens were 0.64 mg/cm2 and 0.59 mg/cm2 respectively. The excellent oxidation resistance of both type(a) and type(b) MoSi2 coated samples at 1200 °C was due to the formation of a dense and continuous SiO2 scale during oxidation. As the CTE mismatch between the outer MoSi2 coating and the inner layer, cracks distributed within both type(a) and type(b) MoSi2 coating structures.